The present invention relates to a metal-base multilayer circuit substrate, particularly a metal-base multilayer circuit substrate which has good noise shielding properties and voltage withstanding properties and which is excellent in heat dissipation properties, and a process for its production.
In recent years, with respect to circuit substrates for mounting semiconductors, downsizing, high density packaging and high performance of circuit substrates are required. Further, as the downsizing, high performance and high power trend of semiconductor devices to be mounted on circuit substrates progress, how to dissipate the heat generated by the semiconductor devices has become an important issue.
Mainly in the field of power source, metal-base circuit substrates are being used for the reason that they are excellent in heat dissipation properties. However, such metal-base circuit substrates have a structure wherein metal foils are laminated by means of insulating layers on a metal plate to form circuits, and accordingly, they have had a problem that noises are likely to be generated, and malfunction of the modules is likely to occur.
For the purpose of accomplishing high density packaging by improving heat dissipation properties while shielding noises, a metal-base multilayer circuit substrate has been proposed (Japanese Unexamined Patent Publication No. 327169/1993) wherein an upper layer circuit substrate having circuits on both sides, is laminated by means of an adhesive on the entire surface or a part of a metal-base circuit substrate, and a heat emissive electronic device is mounted on the upper layer circuit substrate.
However, in such a metal-base multilayer circuit substrate, an adhesive layer made of a resin which has a poor heat conductivity, is present between the metal plate and the upper layer circuit substrate, and as the base material, a material having poor heat dissipation properties, such as an epoxy-impregnated glass cloth, is used. Accordingly, when a heat emissive electronic device is mounted on the upper layer circuit of the circuit substrate, there has been a problem that the heat dissipation properties are inadequate, the temperature of the electronic device increases, and malfunction of the module is likely to occur.
The present inventors have conducted various studies with an aim to solve the above problems and as a result, have found it possible to solve the above problems by using an insulating adhesive which has electrical insulating properties, adhesive properties and heat dissipating properties simultaneously and by adopting a structure having no adhesive layer. The present invention has been accomplished on the bases of this discovery.
It is an object of the present invention to provide a metal-base multilayer circuit substrate excellent in heat dissipating properties and voltage withstanding properties by studying and properly setting the structure of the metal-base multilayer circuit substrate and the heat conductivity of an insulating adhesive layer constituting it, and to provide a process whereby such a circuit substrate can be produced with high productivity.
The present invention provides a metal-base multilayer circuit substrate which comprises a metal plate and a circuit substrate bonded thereon by means of a first insulating adhesive layer containing at least one of metal oxides and/or at least one of metal nitrides.
In such a metal-base multilayer circuit substrate, the first insulating adhesive layer preferably has a heat conductivity of from 35xc3x9710xe2x88x924 cal/cmxc2x7secxc2x7xc2x0C. to 150xc3x9710xe2x88x924 cal/cmxc2x7secxc2x7xc2x0C. and a thickness of from 20 xcexcm to 200 xcexcm.
Further, the present invention provides such a metal-base multilayer circuit substrate wherein the metal oxide is aluminum oxide or silicon oxide, and the metal nitride is boron nitride.
Further, the present invention provides the metal-base multilayer circuit substrate according to claim 1, wherein a first circuit conductor layer on the circuit substrate has a surface roughness Rz of from 0.1 xcexcm to 10 xcexcm on its surface facing the first insulating adhesive layer, particularly such a metal-base multilayer circuit substrate wherein the first circuit conductor layer of the circuit substrate is provided with a plated copper layer on its surface facing the first insulating adhesive layer, more particularly such a metal-base multilayer circuit substrate wherein the plated copper layer contains at least either nickel or cobalt.
Further, the present invention provides the metal-base multilayer circuit substrate according to claim 1, wherein the circuit substrate comprises at least two circuit conductor layers which are bonded by means of a second insulating adhesive layer containing at least one of metal oxides and/or at least one of metal nitrides, preferably such a metal-base multilayer circuit substrate wherein the second insulating adhesive layer has a heat conductivity of from 35xc3x9710xe2x88x924 cal/cmxc2x7secxc2x7xc2x0C. to 150xc3x9710xe2x88x924 cal/cmxc2x7secxc2x7xc2x0C. and a thickness of from 40 xcexcm to 200 xcexcm.
Further, the present invention provides the metal-base multilayer circuit substrate according to claim 1, wherein a heat emissive electronic device is mounted on the first insulating adhesive layer by means of a highly heat conductive adhesive, particularly such a metal-base multilayer circuit substrate wherein a metal layer is provided between the first insulating adhesive layer and the highly heat conductive adhesive.
Further, the present invention provides a process for producing a metal-base multilayer circuit substrate as defined in claim 1, which comprises:
(1) a step of bonding a second circuit conductor layer by means of a second insulating adhesive layer on at least a first circuit conductor layer of a metal-base circuit substrate comprising a metal plate and the first circuit conductor layer formed on the metal plate by means of a first insulating adhesive layer,
(2) a step of forming a through-hole for electrically connecting the second circuit conductor layer and the first circuit conductor layer, and
(3) a step of forming a circuit in the second circuit conductor layer. Preferably in such a process for producing a metal-base multilayer circuit substrate, the first insulating adhesive layer is heat-cured prior to step (2).
Further, the present invention provides such a process for producing a metal-base multilayer circuit substrate, wherein in step (2) for forming the through-hole, a predetermined portion of the second circuit conductor layer is removed by etching to form a hole, and a laser beam is irradiated through the hole to remove the second insulating adhesive layer to form a through-hole, particularly such a process for producing a metal-base multilayer circuit substrate wherein the first circuit conductor layer has a thickness of from 5 xcexcm to 150 xcexcm.
In addition, the present invention provides a semiconductor module which comprises a metal-base multilayer circuit substrate as defined in claim 8 and a semiconductor device mounted thereon and wire-bonded by an aluminum wire or a gold wire, preferably such a semiconductor module wherein the first circuit conductor layer facing the first insulating adhesive layer of the circuit substrate is used as a shield pattern.